Group 13 Lewis acid catalyzed synthesis of metal oxide nanocrystals hydroxide transmetallation

• Published in: Nanoscale 2021-07, Vol.13 (26), p.1155-11517
• Main Authors: Gibson, Noah J, Bredar, Alexandria R. C, Chakraborty, Nilave, Farnum, Byron H
• Format: Article
• ISSN: 2040-3364; 2040-3372
• DOI: 10.1039/d1nr02397g

A new transmetallation approach is described for the synthesis of metal oxide nanocrystals (NCs). Typically, the synthesis of metal oxide NCs in oleyl alcohol is driven by metal-based esterification catalysis with oleic acid to produce oleyl oleate ester and M-OH monomers, which then condense to form M x O y solids. Here we show that the synthesis of Cu 2 O NCs by this method is limited by the catalytic ability of copper to drive esterification and thus produce Cu + -OH monomers. However, inclusion of 1-15 mol% of a group 13 cation (Al 3+ , Ga 3+ , or In 3+ ) results in efficient synthesis of Cu 2 O NCs and exhibits size/morphology control based on the nature of M 3+ . Using a continuous-injection procedure where the copper precursor (Cu 2+ -oleate) and catalyst (M 3+ -oleate) are injected into oleyl alcohol at a controlled rate, we are able to monitor the reactivity of the precursor and M 3+ catalyst using UV-visible and FTIR absorbance spectroscopies. These time-dependent measurements clearly show that M 3+ catalysts drive esterification to produce M 3+ -OH species, which then undergo transmetallation of hydroxide ligands to generate Cu + -OH monomers required for Cu 2 O condensation. Ga 3+ is found to be the "goldilocks" catalyst, producing NCs with the smallest size and a distinct cubic morphology not observed for any other group 13 metal. This is believed to be due to rapid transmetallation kinetics between Ga 3+ -OH and Cu + -oleate. These studies introduce a new mechanism for the synthesis of metal oxides where inherent catalysis by the parent metal ( i.e. copper) can be circumvented with the use of a secondary catalyst to generate hydroxide ligands. Group 13 Lewis acids catalyze the formation of Cu 2 O nanocrystals through a unique transmetallation step involving hydroxide ligands.